Nitric oxide adsorption at Pt(100) electrode surfaces

Nitric oxide adlayers formed at Pt(100) electrode surfaces have been charac terized in situ by means of electrochemical and FTIR spectroscopic experime nts. These adlayers can be reductively stripped from the electrode surface yielding dissolved ammonium as the main reduction product in acidic solutio n. From the voltammetric charge involved in this process the absolute NO co verage for the saturated adlayers has been calculated to be 0.5. This value agrees with that corresponding to the c(4 x 2) overlayer found by differen t authors under UHV conditions. The oxidation of the NO adlayer in acid med ia proceeds between 0.90 and 1.10 V RHE through the formation of surface sp ecies (probably a mixture of nitrite and nitro species), which can be furth er oxidized to dissolved nitrate anions at higher potentials. The same NO a dlayers have been found to oxidize directly to dissolved nitrite anions in alkaline solutions. The potential dependence of the N-O stretching mode, wh ich is shifted towards higher wavenumbers when the electrode potential incr eases, has been analyzed for the saturated NO adlayer. Linear relations wer e found both in acidic and neutral solutions with tuning rates of ca. 59 cm (-1) V-1 in the potential region between 0.50 and 0.90 V RHE where the satu rated NO adlayers are stable. A slow dissolution process has been evidenced at potentials slightly below 0.80 V for the NO adlayer in alkaline solutio ns. (C) 1998 Elsevier Science Ltd. All rights reserved.